How do i file a w2 from 2018 if it wasn't filed yet

The 2018 W-2 can Only be entered on a 2018 tax return.

You can only file a 2018 W-2 with a 2018 tax return or a 2018 amended return if you already filed 2018.   2018 can only be done using the 2018 desktop software and mailed.

You can purchase 2018 software here.

https://turbotax.intuit.com/personal-taxes/past-years-products/

To complete and file a 2018 tax return using TurboTax you would need to purchase, download and install on a personal computer, Win or Mac, one of the 2018 desktop editions from this website - https://turbotax.intuit.com/personal-taxes/past-years-products/

A 2018 tax return can only be printed and mailed, it cannot be e-filed.